Field of the Invention
The present invention relates to droplet deposition apparatus. It may find particularly beneficial application in a drop-on-demand ink-jet printhead, or, more generally, in droplet deposition apparatus and, specifically, in droplet deposition apparatus comprising a manifold component and one or more actuator components, the actuator components providing an array of fluid chambers, which each have a piezoelectric actuator element and a nozzle, the piezoelectric actuator element being operable to cause the release in a deposition direction of fluid droplets through the nozzle in response to electrical signals, where the manifold component includes a first manifold chamber and a second manifold chamber, the first manifold chamber being fluidically connected to said second manifold chamber via each of said fluid chambers in said first array.
Related Technology
Those skilled in the art will appreciate that a variety of alternative fluids may be deposited by droplet deposition apparatus: droplets of ink may travel to, for example, a paper or other substrate, such as ceramic tiling, to form an image, as is the case in inkjet printing applications; alternatively, droplets of fluid may be used to build structures, for example electrically active fluids may be deposited onto a substrate such as a circuit board so as to enable prototyping of electrical devices, or polymer containing fluids or molten polymer may be deposited in successive layers so as to produce a prototype model of an object (as in 3D printing). Droplet deposition apparatus suitable for such alternative fluids may be provided with modules that are similar in construction to standard inkjet printheads, with some adaptations made to handle the specific fluid in question.
In addition, a wide variety of constructions exist within the prior art for droplet deposition, including a number that have been disclosed by the present Applicant. Of particular interest in the present case are the examples provided by WO 00/38928, from which FIGS. 1, 2, 3, 4 and 7 are taken.
WO 00/38928 provides a number of examples of droplet deposition apparatus having an array of fluid chambers, with each chamber communicating with an orifice for droplet ejection, with a common fluid inlet manifold and with a common fluid outlet manifold and where there is, during use, a fluid flow into the inlet manifold, through each chamber in the array and into the outlet manifold.
FIG. 1 illustrates a “pagewide” printhead 10, having two rows of nozzles 20, 30 that extend (in the direction indicated by arrow 100) the width of a piece of paper and which allow ink to be deposited across the entire width of a page in a single pass. Ejection of ink from a nozzle is achieved by the application of an electrical signal to actuation means associated with a fluid chamber communicating with that nozzle, as is known e.g. from EP-A-0 277 703, EP-A-0 278 590, WO 98/52763 and WO 99/19147.
More particularly, as taught in EP-A-0 277 703 and EP-A-0 278 590, piezoelectric actuator walls may be formed between successive channels and are actuated by means of electric fields applied between electrodes on opposite sides of each wall so as to deflect transversely in shear mode. The resulting pressure waves generated in the ink or other fluid cause ejection of a droplet from the nozzle.
To simplify manufacture and increase yield, the “pagewide” row(s) of nozzles may be made up of a number of modules, one of which is shown at 40, each module having associated fluid chambers and actuation means and being connected to associated drive circuitry (integrated circuit (“chip”) 50) by means e.g. of a flexible circuit 60. Ink supply to and from the printhead is via respective bores (not shown) in end-caps 90.
FIG. 2 is a perspective view of the printhead of FIG. 1 from the rear and with end-caps 90 removed to reveal the supporting structure 200 of the printhead incorporating ink flow passages, or manifolds 210,220,230 extending the width of the printhead.
WO 00/38928 teaches that ink may be fed into an inlet manifold and out of an outlet manifold, with the manifolds being common to and connected via each channel, so as to generate ink flow through each channel (and thus past each nozzle) during printhead operation. This may act to prevent the accumulation of dust, dried ink or other foreign bodies in the nozzle that would otherwise inhibit ink droplet ejection.
In more detail, ink enters the printhead of FIGS. 1 to 4 via a bore in one of the end-caps 90 (omitted from the views of FIGS. 1 and 2), and via the inlet manifold 220, as shown at 215 in FIG. 2. As it flows along the inlet manifold 220, it is drawn off into respective ink chambers, as illustrated in FIG. 3, which is a sectional view of the printhead taken perpendicular to the direction of extension of the nozzle rows. From inlet manifold 220, ink flows into first and second parallel rows of ink chambers (indicated at 300 and 310 respectively) via aperture 320 formed in structure 200 (shown shaded). Having flowed through the first and second rows of ink chambers, ink exits via apertures 330 and 340 to join the ink flow along respective first and second ink outlet passages 210,230, as indicated at 235. These join at a common ink outlet bore (not shown) formed in the end-cap and that may be located at the opposite or same end of the printhead to that in which the inlet bore is formed.
Each row of chambers 300 and 310 has associated therewith respective drive circuits 360,370. The drive circuits are mounted in substantial thermal contact with that part of structure 200 acting as a conduit and which defines the ink flow passageways so as to allow a substantial amount of the heat generated by the circuits during their operation to transfer via the conduit structure to the ink. To this end, the structure 200 is made of a material having good thermal conduction properties. WO 00/38928 teaches that aluminum is a particularly preferred material, on the grounds that it can be easily and cheaply formed by extrusion. Circuits 360,370 are then positioned on the outside surface of the structure 200 so as to lie in thermal contact with the structure, thermally conductive pads or adhesive being optionally employed to reduce resistance to heat transfer between circuit and structure.
In order to reinforce the support structure 200, a bar made from a strong material, such as steel, may be provided within channel 550 (as is known from WO 00/2584).
Further detail of the chambers and nozzles of the particular printhead shown in FIGS. 1 to 3 is given in FIG. 4, which is a sectional view taken along a fluid chamber of a module 40. As shown in FIG. 4, channels 11 are machined or otherwise formed in a base component 860 of piezoelectric material so as to define piezoelectric channel walls which are subsequently coated with electrodes, thereby to form channel wall actuators, as known e.g. from EP-A-0 277 703. Each channel half is closed along a length 600,610 by respective sections 820,830 of a cover component 620 which is also formed with ports 630,640,650 that communicate with fluid manifolds 210,220,230 respectively. Each half 600,610 of the channel 11 thus provides one fluid chamber.
A break in the electrodes at 810 allows the channel walls in either half of the channel to be operated independently by means of electrical signals applied via electrical inputs (flexible circuits 60). Ink ejection from each channel half is via openings 840,850 that communicate the channel with the opposite surface of the piezoelectric base component to that in which the channel is formed. Nozzles 870,880 for ink ejection are subsequently formed in a nozzle plate 890 attached to the piezoelectric component.
The large arrows in FIG. 4 illustrate (from left to right): the flow of fluid from the chambers on the left-hand-side of the array 600 to outlet manifold 210, via the left-hand port 630; the flow of fluid into the channels from inlet manifold 220, via the central port 640; and the flow of fluid from the chambers on the right-hand-side of the array 610 to the other outlet manifold 230, via the right-hand port 650.
As a result, it will be appreciated that there is, during use of the printhead, a flow of fluid along the length of each of the chambers 600,610. As noted above, WO 00/38928 teaches that this ink flow through each channel (and thus past each nozzle) during printhead operation may act to prevent the accumulation of dust, dried ink or other foreign bodies in the nozzle that would otherwise inhibit ink droplet ejection. More, WO 00/38928 teaches that, to ensure effective cleaning of the chambers by the circulating ink and in particular to ensure that any foreign bodies in the ink, e. g. dirt particles, are likely to go past a nozzle rather than into it, the ink flow rate through a chamber must be higher than the maximum rate of ink ejection from the chamber and may, in some cases, be ten times that rate.
FIGS. 5 and 6 are exploded perspective views (taken from WO 01/12442) of a printhead having similar features as that shown in FIGS. 1 to 4. Thus, WO 01/12442 provides further examples of droplet deposition apparatus having an array of fluid chambers, with each chamber communicating with an orifice for droplet ejection, with a common fluid inlet manifold and with a common fluid outlet manifold and where there is, during use, a fluid flow into the inlet manifold, through each chamber in the array and into the outlet manifold.
FIGS. 5 and 6 illustrate in detail how various components may be arranged on a substrate 86, together with constructional details of the substrate 86 itself.
In more detail, FIGS. 5 and 6 illustrate two rows of channels spaced relative to one another in the media feed direction. The two rows of channels are formed in respective strips of piezoelectric material 110a, 110b, which are bonded to a planar surface of substrate 86. Each row of channels extends the width of a page in a direction transverse to the media feed direction. As discussed above, electrodes are provided on the walls of the channels, so that electrical signals may be selectively applied to the walls. The channel walls may thus act as actuator members that can cause droplet ejection.
Substrate 86 is formed with conductive tracks 192, which are electrically connected to the respective channel wall electrodes, (for example by solder bonds), and which extend to the edge of the substrate where respective drive circuitry (integrated circuits 84) for each row of channels is located.
As may also be seen from FIGS. 5 and 6, a cover member 420 is bonded to the tops of the channel walls so as to create closed, “active” channel lengths which may contain pressure waves that allow for droplet ejection. Holes are formed in cover member 420 that communicate with the channels to enable ejection of droplets. These holes in turn communicate with nozzles (not shown) formed in a nozzle plate 430 attached to the planar cover member 420. However, it is also known, for example from WO 2007/113554, to use an appropriately constructed nozzle plate in place of such a combination of a cover member and nozzle plate.
As with the construction described with reference to FIGS. 1 to 4, the substrate 86 is provided with ports 88, 90 and 92, which communicate to inlet and outlet manifolds. The inlet manifold may be provided between two outlet manifolds, with the inlet manifold thus supplying ink to the channels via port 90, and ink being removed from the two rows of channels to respective outlet manifolds via ports 88 and 92. As FIG. 6 illustrates, the conductive tracks 192 may be diverted around the ports 88, 90 and 92.
It is known from WO 00/38928 for the cross-sectional area of the manifolds to taper with increasing distance in the direction of the array. The arrangements discussed in WO 00/38928 are intended to be applied to printheads in which the linear array of droplet fluid chambers is arranged at a non-zero angle to the horizontal direction. Accordingly, the taper results, in each manifold, in the viscous pressure drop per length down the array being balanced against the gravitational increase in pressure. This is achieved by arranging that the cross-section available for flow at each point is appropriate to the flow there.
FIG. 7, which is taken from WO 00/38928, schematically illustrates an arrangement where a linear array of droplet fluid chambers of similar construction to that discussed with reference to FIGS. 1 to 6 is arranged at a non-zero angle to the horizontal direction (i. e. at a non-perpendicular angle to the direction of gravity, indicated by arrow X in the figure). For the sake of clarity, only a single linear array of chambers is depicted by arrows 1000. However, the constructions disclosed in WO 00/38928 utilize an arrangement having a single inlet manifold 1010 and double outlet manifolds 1020, as shown in FIGS. 1-4. Manifolds 1010,1020 are supplied with and drained of ink at connections 1030 and 1040 respectively.
More particularly, as shown in FIG. 7, inserts 1050 and 1060 having a tapered shape are respectively placed in inlet 1010 and outlet 1020 manifolds, which have a generally constant rectangular cross-section. As a result, the ink entering the inlet manifold 1010 at the top of the array finds that the tapered insert 1050 only blocks part of the cross-section of the manifold. As the ink passes down the inlet manifold 1010, some of it flows outwards via the fluid chambers 1000 to the outlet manifold 1020 such that, by the time the bottom of the array is reached, there is no ink flowing in the inlet manifold 1010 and the tapered insert 1050 leaves no cross-section for flow. Ink reaching the outlet manifold 1020 also flows downwards, via cross-sections which increase towards the bottom by virtue of further tapered inserts 1060. By the bottom of the array, all the ink (except that which has been ejected for printing) is flowing in the large space allowed by the inserts.
Although the arrangements discussed in WO 00/38928 are intended to be applied to printheads in which the linear array of droplet fluid chambers is arranged at a non-zero angle to the horizontal direction, so as to balance the decrease in viscous pressure against the increase in gravitational pressure along the array, there may be a number of reasons for providing a taper within the manifolds.
In particular, providing a taper within the manifolds may assist with purging of the fluid chambers as part of a start-up mode for the apparatus. For example, the taper may ensure a roughly equal amount of fluid flow passes through each of the chambers in the array. This may, for example, reduce the likelihood of bubbles being trapped at the end of the array furthest from the point where enters the manifold. In order to provide such functionality, the direction of the taper in the inlet and outlet manifolds may be broadly similar to that shown in FIG. 7, though it will of course be appreciated that the different purpose for the taper will significantly impact upon the exact rate at which the cross-sectional area tapers with respect to distance in the array direction.
In droplet deposition apparatus it is generally desirable to improve the uniformity over the length of the array of the droplets deposited; this is particularly the case with droplet deposition apparatus that have a large array of fluid chambers, such as inkjet printers. Where a substrate is indexed past the array of fluid chambers to produce a pattern of droplets on the substrate (for example forming an image on a sheet of paper or a ceramic tile) such non-uniformity over the length of the array may be particularly visible, since it will produce generally linear defects extending in the direction of substrate movement, the human eye being particularly adept at identifying such linear features.
However, even where the pattern formed is not intended to be viewed by the human eye (such as where electrically active fluids are deposited onto a substrate such as a circuit board so as to enable prototyping of electrical devices, or polymer containing fluids or molten polymer may be deposited in successive layers so as to produce a prototype model (so-called 3D printing)), or where the substrate is not indexed past the array, it will still be appreciated that non-uniformity over the length of the array will be a concern.
There are numerous factors that are thought to cause non-uniformity of deposited droplets, with the interactions between these factors complex and often difficult to predict.